Exhaust casing, and steam turbine provided with same

An exhaust casing which is configured to guide steam flowing out of a last rotor blade row of a steam turbine rotor rotating about an axis to an outside, the exhaust casing comprising:

• a diffuser into which the steam flowing out of the last rotor blade row flows and which has an annular shape with respect to the axis, and forms a diffuser space directed gradually to a radially outer side with respect to the axis toward an axially downstream side;
• and
• an outer casing which has an exhaust port opening toward the radially outer side, communicates with the diffuser, and widens an outer circumference of the diffuser in a circumferential direction with respect to the axis to form an exhaust space which is configured to guide the steam flowing in from the diffuser space to the exhaust port,
• wherein the diffuser has:
• an outer diffuser which has an annular cross section perpendicular to the axis and gradually widens to the radially outward toward the axially downstream side to define an edge on the radially outer side of the diffuser space, and
• an inner diffuser which has an annular cross section perpendicular to the axis, and gradually widens to the radially outward toward the axially downstream side to define an edge on a radially inner side of the diffuser space with respect to the axis,
• the outer casing has:
• a downstream side end plate which widens to the radially outward from the edge on the radially outer side of the inner diffuser to define an edge on the axially downstream side of the exhaust space,
• an inclined plate which is disposed on the side radially outward from the downstream side end plate in a region on a side opposite to the exhaust port on the basis of the axis, and gradually widens to an axially upstream side toward the radially outer side to define a part of the edge on the radially outer side of the exhaust space, and
• a side peripheral plate connected to the downstream side end plate and the inclined plate, and widens in the circumferential direction about the axis to define another part of the edge on the radially outer side of the exhaust space,
• in the inclined plate, an edge on the axially upstream side at a position diametrically opposite to the exhaust port on the basis of the axis is located on the axially upstream side, on the basis of a virtual plane which widens from an end on the radially outer side of the outer diffuser and is parallel to the downstream side end plate, and
• an angle of an inclined inner surface defining the exhaust space by the inclined plate with respect to a tangential line at the end on the radially outer side of the inner peripheral surface of the outer diffuser, which is an upstream side angle on the axially upstream side on the basis of the tangential line in the exhaust space, is greater than an angle of the inclined inner surface with respect to the tangential line, which is a downstream side angle on the axially downstream side on the basis of the tangential line in the exhaust space.